A high-fiber diet vs metformin: a small trial in China found that adults with newly diagnosed type 2 diabetes and obesity who ate a high-fiber diet for 84 days ended with a lower HbA1c (6.3%) than those taking the drug (6.7%). It is an eye-catching result, but it comes from one hospital, a few dozen people and a study design with real limits. Here is what the trial found, what it does not prove, and how to add fiber safely. This is general information, not medical advice.
What the high-fiber diet vs metformin trial tested
The study was published in Frontiers in Microbiology (volume 17, 2026) by Li Y, Liu Y, Chen Y and colleagues, and News-Medical summarized it on Oct. 7, 2026. It was a head-to-head comparison run at a single center, Henan Provincial People’s Hospital in China, over 84 days.
Participants were adults aged 18 to 70 with newly diagnosed type 2 diabetes and obesity. Their HbA1c was between 6.5% and under 9.0%, and their BMI was 24 or higher. After a two-week run-in period, 48 adults were included in the comparison.
One group followed a high-fiber diet with no diabetes medication. The other took metformin, a widely prescribed first-line drug for type 2 diabetes.
How many people were in each group
The groups were not equal in size, and that matters when you weigh the result.
- High-fiber group: 36 people were randomized and 34 completed the trial.
- Metformin group: 12 people were randomized and all 12 completed it.
- Total completers: 46 adults.
The fiber group used high-fiber formulas that combined soluble and insoluble fibers, including inulin and resistant dextrin. The amount in grams per day was not stated in the summary we reviewed.
The results: blood sugar, weight and fats
At day 84, after adjusting for baseline values, the fiber group had a lower HbA1c than the metformin group: 6.3% versus 6.7%. BMI was also lower in the fiber group, at 28.4 versus 30.2.
The fiber group also showed lower glycemic variability on continuous glucose monitoring (CGM), lower fat mass and lower triglycerides, according to the News-Medical report.
One caveat is built into the data. The fiber group consumed less energy, meaning fewer calories, and that may have contributed to the weight and blood sugar changes. The trial summary does not separate the effect of fiber itself from the effect of eating less.
What is HbA1c, and what does open-label mean?
HbA1c is a blood test that reflects your average blood sugar over roughly the past two to three months. A lower number generally means better control. Doctors often use it to track diabetes.
Open-label means participants and researchers knew who was getting which treatment. Nobody was blinded. That can influence results, because people who know they are on a special diet may change other habits too.
Glycemic variability describes how much glucose swings up and down during the day. A CGM is a small sensor that tracks those swings continuously.
High-fiber diet vs metformin: how to read the numbers
A gap of 0.4 percentage points in HbA1c (6.3% versus 6.7%) sounds small, but in diabetes care it can matter. Still, the figures are baseline-adjusted group averages from a small trial, so individual results will vary widely.
The study also compared two very different things. One was a structured, supervised diet. The other was a pill taken at standard care. Eating a planned high-fiber diet under trial supervision is not the same as what most people manage at home, where adherence tends to slip over time.
It also helps to remember what metformin does well. It is inexpensive, widely studied over many years, and backed by long-term safety data. A short trial does not erase that track record, and the fiber results would need to be repeated before guidelines could change.
For readers without a diabetes diagnosis, the practical message is gentler: most adults can benefit from more fiber, and few eat enough. For readers with a diagnosis, the message is to ask whether fiber can sit alongside the treatment you already have.
The gut microbiome findings
Your microbiome is the community of bacteria and other microbes in your gut. In this trial, the fiber diet changed that community within 28 days.
The fiber group saw more Bifidobacterium and Lactobacillus, two groups of bacteria often discussed as beneficial. It also saw less Bilophila wadsworthia, a bacterium linked to inflammation. The metformin group showed no significant overall shift in its microbiome, per the report.
These are associations observed in a small sample. The summary does not show that the bacterial changes caused the better blood sugar numbers. Related gut research is covered in our look at sugar, antibiotics and the gut microbiome.
Why the high-fiber diet vs metformin result is not a green light to stop medicine
This trial does not show that fiber replaces metformin. It does not mean anyone should stop or skip diabetes medicine. Most people with diabetes should not change their treatment without talking to their clinician first.
The authors and the News-Medical summary point to several limits:
- Single center: results from one hospital in China may not apply to other populations.
- Small size: 48 adults is a modest sample.
- Few on metformin: only 12 people took the drug, against 36 in the fiber group.
- Short duration: 84 days says little about long-term control or complications.
- GLP-1 not measured: a gut hormone involved in blood sugar regulation was not assessed.
- Exploratory subgroups: some analyses were not planned as primary tests.
The people studied also had newly diagnosed disease. Results may differ for those who have lived with diabetes for years or who need stronger treatment. No named researcher quotes were available in the source, so we are not attributing any.
How to raise fiber the practical way
You do not need special formulas to start. General US dietary guidance puts adult fiber targets at roughly 25 to 38 grams a day, depending on age and sex, though exact figures vary by source. Many Americans eat well below that.
Add fiber gradually to avoid gas and bloating. A simple approach:
- Week 1: swap one refined grain a day for a whole grain such as oats, brown rice or whole-wheat bread.
- Week 2: add a serving of beans, lentils or chickpeas to a meal.
- Week 3: make two daily snacks a fruit with skin, raw vegetables or a small handful of nuts.
- Week 4: add vegetables to every lunch and dinner, and keep going.
Drink plenty of water as fiber goes up, since fiber works best with enough fluid. Check nutrition labels, which list fiber in grams per serving.
Good sources include beans, lentils, oats, berries, apples, pears, broccoli, chia and flax seeds, and whole grains. Inulin, one fiber used in the trial, also occurs naturally in foods such as chicory root, onions and garlic.
If you take diabetes medicine, tell your care team before making big diet changes. Blood sugar can shift, and doses sometimes need adjusting. The CDC’s diabetes resources cover healthy eating and management basics.
Another way to think about the high-fiber diet vs metformin question is that the two are not necessarily rivals. Many clinicians already pair medication with nutrition and activity changes, and nothing in this trial tests that combination. That is a gap future studies could fill.
What to watch next
The next step is larger, longer and blinded or better-controlled trials, ideally with more people on metformin and a clear fiber dose. Until then, treat this study as a promising early signal rather than a new treatment rule.
For more on lifestyle approaches, see our report on type 2 diabetes remission with diet and exercise and our piece on how olive oil before carbs affected blood sugar in mice.
The takeaway
The high-fiber diet vs metformin trial suggests that food can move blood sugar markers in a meaningful way, at least in the short term. It does not suggest you should drop your medicine.
Your action step this week: look at one meal and add a fiber-rich food, then book a visit or message your clinician if you want to discuss diet alongside your treatment plan. This article is for information only and is not a substitute for medical advice.
